Magical Jelly is the best product key
finder for Windows. It’s free and
portable, hence you can use it without
installation or modifying the Windows
registry. It can be used to extract
the product keys of paid software like
Microsoft Office, Microsoft Visual
Studio, Adobe Photoshop etc.

You could try ProduKey from NirSoft. Its an app for listing Microsoft licence keys, however I don't think it'll work if your copy of Visual Studio was pre-pidded, i.e. it came from say an MSDN account.

What does pre-pidded mean? Does it mean that key was embedded right into the image or cd that was downloaded?
– spongApr 14 '10 at 14:07

@sunpech - that's exactly what it means. If you download an ISO from MSDN or use MSDN media the key is already set and you don't have to enter it. This is specific to Visual Studio (and some other MS products), Office Suites/Apps and Operating Systems do not come pre-pidded.
– ShevekApr 14 '10 at 14:13

with an embedded key, how does microsoft know then if there are multiple installs with that media?
– spongApr 14 '10 at 14:25

1

@sunpech: the one I linked to in my answer pulls pre-pidded product keys. My VS2008 is from MSDN and it found it just fine.
– squillmanApr 14 '10 at 14:30

pre-pidded keys are exactly the same as serial keys you entered yourself. They've just been filled in for you already by Microsoft. They are generated dynamically and inserted into the ISO you download from Microsoft. So they know exactly what the key is and which MSDN account the key was issued to.
– BBlakeApr 14 '10 at 15:01

I've had positive experiences with Belarc Advisor http://www.belarc.com/Programs/advisor.exe. It gives out a neat list of software installed on your pc with Keys and I generally archive this on a secure cloud so even if My pc crashes, I can still get a registered copy of all the software installed.

Today its even possible to have the entire image of your installation archived so that You get a clean PC with the set of licenses refreshed on installed anytime you want one!